The present invention relates to the electric braking of a transit vehicle with a brake effort request P signal indicating the desired brake effort, and with the receptivity of the power supply line determining how much electric braking energy is regenerated to the power supply line and how much is dissipated in the dynamic braking resistors.
In an article entitled "Propulsion Control for Passenger Trains Provides High Speed Service" that was published in the Westinghouse Engineer for September, 1970 at pages 143-149 there is discussed the operation of the P signal to establish the requested brake effort in the brake mode of operation.
In an article entitled "Alternative Systems for Rapid Transit Propulsion and Electrical Braking" that was published in the Westinghouse Engineer for March, 1973 at pages 34-41 there is discussed the thyristor chopper operation for dynamic braking, with the generating motors providing output current that is either returned to the supply line or dissipated in a dynamic braking resistor by turning on the thyristor T5 shown in that article. The thyristor chopper is fast enough to match regenerated voltage-to-line voltage.
Electric braking effort depends upon the kinetic energy stored in the vehicle and employs the propulsion motors to generate electrical energy that is regenerated back to the power supply line or is dissipated in provided resistors as a function of the current that flows in the resistors. At higher vehicle speeds since the back EMF of the motors is high, more effective electric braking can be provided then at lower speeds. Therefore, when electric braking as compared with mechanical friction braking is to be provided, it is usually desirable first to apply more of the electric braking at higher speed and as the vehicle slows down, then to apply more of the mechanical friction braking.
It is known in the prior art to monitor the line filter capacitor voltage to determine the receptivity of the power supply line for such regenerative power such that if the capacitor voltage goes above a preset limit, then the regenerative braking to the power supply line is terminated and either dynamic braking or friction braking is used to stop the vehicle as disclosed in U.S. Pat. No. 3,657,625 of Miller et al. and U.S. Pat. No. 3,593,089 of Appelo.
It is known in the prior art as disclosed in U.S. Pat. No. 4,123,693 of L. W. Anderson et al. to provide a programmed microprocessor to sense the line voltage and control the current that is generated by the vehicle motor in the brake mode in relation to at least one predetermined limit of the power supply line voltage.